Not all sounds made by animals serve as language,
and we have only to turn to
that extraordinary discovery of echo-location in bats to see a case
in which the
voice plays a strictly utilitarian role.
To get a full appreciation of what this means we must turn first to
human inventions. Everyone knows that if he shouts in the vicinity
of a wall or
a mountainside, an echo will come back. The further off this solid
the longer time will elapse for the return of the echo. A sound made
on the hull of a ship will be reflected from the sea bottom, and by
time interval between the taps and the receipt of the echoes the
depth of the
sea at that point can be calculated. So was born the echo-sounding
now in general use in ships. Every solid object will reflect a
sound, varying according
to the size and nature of the object. A shoal of fish will do this.
So it is a
comparatively simple step from locating the sea bottom to locating a
fish. With experience, and with improved apparatus, it is now
possible not only
to locate a shoal but to tell if it is herring, cod, or other
well-known fish, by the
pattern of its echo.
A few years ago it was found that certain bats emit squeaks and by
the echoes they could locate and steer clear of obstacles--or locate
on which they feed. This echo-location in bats is often compared
with radar, the
principle of which is similar.
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